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Effect of Moisture Absorption on the Flexural Properties of Basalt/CNT/Epoxy Composites Man-Tae Kim1, Kyong-Yop Rhee2,♠, Hyeon-Ju Kim3 and Dong-Ho Jung3

1Department of R&D, Gumi Electronics & Infomation Technology Research Institute, Gumi, 730-853, Korea 2School of Mechanical Engineering, Kyung Hee University, Yongin 446-701, Korea3Ocean Pant Research Division, Korea Institute of Ocean Science & Technology, Daejon 305-600, Korea

Received 7 June 2012Accepted 1 July 2012

*Corresponding AuthorE-mail: rheeky@khu.ac.krTel: +82-31-201-2565

Open Access

pISSN: 1976-4251 eISSN: 2233-4998

Carbon Letters Vol. 13, No. 3, 187-189 (2012)Note

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Copyright © Korean Carbon Society

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AbstractThis study investigates the flexural properties of multi-walled carbon nanotube (MW-CNT) reinforced basalt/epoxy composites under conditions with and without moisture absorption. The basalt/CNT/epoxy composites were fabricated using 1 wt% silanized MWCNTs and kept in seawater for over 4 months. The flexural properties of the mois-ture absorbed specimens were evaluated and compared with those of dry specimens. The flexural properties of basalt/CNT/epoxy composites were found to decrease with mois-ture absorption. The flexural strength and modulus of moisture absorbed specimens were 22% and 16% lower, respectively, than those of the dry specimen. Scanning electron microscope examination of the fracture surfaces revealed that the decreases of flexural properties in the moisture absorbed specimen were due to the weakening of interfacial bonding from swelling of the epoxy matrix.

Key words: basalt/carbon nanotube/epoxy composites, moisture absorption, flexural property

1. Introduction

The increases of economic and environmental demands on reinforced polymer ma-terials are encouraging researchers to develop high strength composite materials. Ba-salt fiber is environmentally harmless and free from carcinogens and other hazardous compounds. It has excellent properties, such as good thermal performance and chemi-cal stability; thus, a number of studies have investigated its mechanical properties and chemical resistance [1-4]. One of the most important issues for polymeric composites is their degradation behavior when exposed to environmental conditions such as humid-ity and temperature. The moisture absorption of the polymer causes plasticization and swelling, weakening the interfacial strength between the epoxy and the reinforcing ma-terials [5,6]. Currently, many studies have been performed to investigate the mechani-cal properties of multiscale composites because such multiscale composites are known to have mechanical performances better than those of conventional composites [7-10]. However, little research has been performed to investigate the effect of moisture absorp-tion on the mechanical behavior of multiscale composites [11].

In this study, we have investigated the effect of moisture absorption on the flex-ural behavior of basalt/carbon nanotube (CNT)/epoxy composites. Flexural tests were performed using basalt/CNT/epoxy composites with and without moisture absorption. Following the flexural tests, scanning electron microscopy (SEM) was used to exam-ine the fracture surfaces to determine the failure mechanisms based on the moisture absorption.

DOI: http://dx.doi.org/ 10.5714/CL.2012.13.3.187

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pISSN: 1976-4251 eISSN: 2233-4998VOL. 13 NO. 3 July 31 2012

Carbon Letters Vol. 13, No. 3, 187-189 (2012)

DOI: http://dx.doi.org/10.5714/CL.2012.13.3.187 188

than that of moisture absorbed specimen. Specifically, the flexural strengths of the dry and moisture-absorbed specimens were 316 MPa and 244 MPa, respectively. Clearly, the reduction in flexural strength after moisture absorption can be related to the weak fi-ber and matrix interface due to seawater absorption. The flexural modulus also decreased for the soaked specimens. The reduction in the flexural modulus for moisture absorbed basalt/CNT/epoxy composites was 16% compared to that value of the dry specimen. A plausible explanation for this would be that the basalt/CNT/epoxy composites have matrix-sensitive properties in composites, and, as a result of stress transfer, the capability across the fiber and matrix interface is sharply reduced by moisture absorption.

Field emission-SEM analysis was performed on the fracture surfaces of the composites to investigate the failure mechanism due to moisture absorption; the results are shown in Fig 3. For the dry specimen (Fig. 3a), it can be seen that the CNTs were well dispersed and impregnated in the epoxy resin. For the mois-ture absorbed specimen (Fig. 3b), it can also be seen that the CNTs were well dispersed in the matrix. However, we can see that many interfacial failures occurred at the interfaces between the matrix and the CNTs, which resulted in the reduced flexural strength and modulus.

2. Experimental

The carbon nanotubes used in this study were multi-walled CNTs, (MWCNTs, CM-95) purchased from Hanhwa Nanotech Co., Ltd., Korea. The diameter and the length of the nanotubes were in the range 10-15 nm and 10-20 μm, respectively and the purity was more than 95%. The reagents used were 3-aminopro-pyltriethoxysilane (99% purity; Aldrich, USA), distilled water (99.5%, Dae Jung Chemical, Korea), acetone (99.5%, Dae Jung Chemical, Korea), and ethanol (99.5%, Sigma-Aldrich). The ep-oxy used was 118.2 g/eq of diglycidyl ether of bisphenol A (YD-115, Kukdo Chemical, Korea) and the hardener was 60 g/eq of polyamidoamine (G-A0533, Kukdo Chemical, Korea).

The fabrication process of the basalt/CNT/epoxy composites was as follows: silane-treated CNTs were mixed with the etha-nol at 1 wt%. Ultrasonication was performed for 5 min for bet-ter dispersion. After sonication, the silane-treated CNTs were mixed with the epoxy resin and then stirred for approximately 2 h at 80ºC to completely evaporate the ethanol. Epoxy resin mixed with hardener (2:1 v/v) was prepared using 1 wt% silanized CNTs. Eight plies of basalt fabric were then impregnated into the matrix, and the basalt/CNT/epoxy composites were cured in an autoclave (ISA-CA30, Ilshin Co., Korea) at 3 kgf/cm2 and 130ºC for 2 h.

The fabricated basalt/CNT/epoxy composite plates were ma-chined as flexural test specimens according to ASTM D790 [12]. Then, the specimens were kept immersed in sterile-filtered seawa-ter (Sigma-Aldrich, S-9148, USA) for up to 4 months. After wiping the surfaces dry, the weights of the moisture absorbed specimens were measured quickly, in order to minimize evaporation losses. Flexural tests were performed using a universal testing machine (Model: 8801, Instron, USA) at a cross-head speed of 1 mm/min.

3. Results and Discussion

The moisture absorption curves of the basalt/CNT/epoxy composites is shown in Fig. 1; in this figure, moisture uptake is plotted against the square root of immersion time. In general, polymer matrix composites are superior to metals in terms of corrosion resistance; however, they are inferior in terms of me-chanical properties after moisture absorption. Additionally, it has been reported that the material characteristics are signifi-cantly affected by the rate of moisture absorption [13]. In this work, the absorption content, “C”, of the basalt/CNT/epoxy multiscale composites was calculated from the weight of the specimens before and after moisture absorption:

(1)

where Ww and Wd represent the weights of the soaked specimen and the dry specimen, respectively. As shown in the figure, an approximately linear relation between the moisture content and the square root of time was observed for the specimens in the initial stage of the absorption process; then, the absorption pro-cess gradually reached an equilibrium state.

Fig. 2 shows the flexural strength and moduli of the dry and moisture absorbed basalt/CNT/epoxy composites. As shown in the figure, the flexural strength of the dry specimen was greater

Fig. 1. Water absorption curves at room temperature for silane-treated basalt/carbon nanotube/epoxy multi-scale composites.

Fig. 2. Flexural strength and modulus of dry and moisture absorbed basalt/carbon nanotube/epoxy composites.

Effect of Moisture Absorption on the Flexural Properties of Basalt/CNT/Epoxy Composites

189 http://carbonlett.org

ram, 58, 62 (2001). http://dx.doi.org/10.1023/a:1010901615857. [2] Singletary J, Davis H, Knoff W, Ramasubramanian MK. Yarns of

basalt continuous fibers. Proceedings of the Fiber Society, Raleigh, NC (2001).

[3] Ozturk S. The effect of fibre content on the mechanical proper-ties of hemp and basalt fibre reinforced phenol formaldehyde com-posites. J Mater Sci, 40, 4585 (2005). http://dx.doi.org/10.1007/s10853-005-1103-z.

[4] Liu Q, Shaw MT, Parnas RS, McDonnell AM. Investigation of basalt fiber composite mechanical properties for applications in transportation. Polym Compos, 27, 41 (2006). http://dx.doi.org/10.1002/pc.20162.

[5] Dhakal HN, Zhang ZY, Richardson MOW. Effect of water absorp-tion on the mechanical properties of hemp fibre reinforced unsatu-rated polyester composites. Compos Sci Technol, 67, 1674 (2007). http://dx.doi.org/10.1016/j.compscitech.2006.06.019.

[6] Roy R, Sarkar BK, Bose NR. Effects of moisture on the mechani-cal properties of glass fibre reinforced vinylester resin composites. Bull Mater Sci, 24, 87 (2001).

[7] Kim MT, Rhee KY. Flexural behavior of carbon nanotube-modi-fied epoxy/basalt composites. Carbon Lett, 12, 177 (2011). http://dx.doi.org/10.5714/CL.2011.12.3.177.

[8] Wang Y, Iqbal Z, Malhotra SV. Functionalization of carbon nano-tubes with amines and enzymes. Chem Phys Lett, 402, 96 (2005). http://dx.doi.org/10.1016/j.cplett.2004.11.099.

[9] Kim MT, Rhee KY, Lee JH, Hui D, Lau AKT. Property enhance-ment of a carbon fiber/epoxy composite by using carbon nano-tubes. Composites Part B: Eng, 42, 1257 (2011). http://dx.doi.org/10.1016/j.compositesb.2011.02.005.

[10] Kim MT, Rhee KY, Park SJ, Hui D. Effects of silane-modified carbon nanotubes on flexural and fracture behaviors of carbon nanotube-modified epoxy/basalt composites. Composites Part B: Eng, 43, 2298 (2012). http://dx.doi.org/10.1016/j.compos-itesb.2011.12.007.

[11] Wan YZ, Wang YL, Huang Y, Luo HL, He F, Chen GC. Mois-ture absorption in a three-dimensional braided carbon/Kevlar/epoxy hybrid composite for orthopaedic usage and its influ-ence on mechanical performance. Composites Part A: Appl Sci Manufact, 37, 1480 (2006). http://dx.doi.org/10.1016/j.compos-itesa.2005.09.009.

[12] ASTM D790-10: Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials. http://dx.doi.org/10.1520/D0790-10.

[13] Kim YH, Park JM, Yoon SW, Lee JW, Jung MK, Murakami RI. The effect of moisture absorption and Gel-coating process on the mechanical properties of the basalt fiber reinforced composite. Int J Ocean Syst Eng, 1, 148 (2011). http://dx.doi.org/10.5574/IJO-SE.2011.1.3.148.

4. Conclusions

The effect of moisture absorption on the flexural properties of basalt/CNT/epoxy composites has been studied. The moisture ab-sorption of specimens matched the predictions of the Fickian mod-el, and the moisture content at full saturation was approximately 1% of the specimen weight. The flexural strength and modulus of the moisture absorbed specimen were 22% and 16% lower, respec-tively, than those values of the dry specimen. The decreases in these values for moisture absorbed specimens were due to the weakening of the interfacial bonding due to swelling of the epoxy matrix.

Acknowledgements

This work was financially supported by the National R&D project of “Development of Energy Utilization of Deep Ocean Water” supported by the Korean Ministry of Land, Traffic and Maritime Affairs.

References

[1] Gur’ev VV, Neproshin EI, Mostovoi GE. The effect of basalt fiber production technology on mechanical properties of fiber. Glass Ce-

Fig. 3. Scanning electron microscope images of the fracture surfaces of dry (a) and moisture absorbed (b) for silane-treated basalt/carbon nano-tube/epoxy composites.